Despite being based on a technology that has not changed substantially in decades, incandescent lamps remain the most widely-used source of in-home lighting. It is thought that this prevalence is due largely to the preference of many people to the warm, yellowish light given off by the incandescent lamps and the relative inexpensiveness of the lights compared to other technologies. Incandescent lights create light by running electricity through a thin filament. The resistance of the filament to the flow of electricity causes the filament to heat to a very high temperature, which produces visible light. Because 98% of the energy input into an incandescent lamp is emitted as heat, however, the process is highly inefficient. Thus, although incandescent lighting is inexpensive and accepted, there has been a push for more efficient lighting technology.
In some applications, particularly in office buildings and retail stores, incandescents have been largely replaced by fluorescent lamps. Fluorescent lamps work by passing electricity through mercury vapor, which in turn produces ultraviolet light. The ultraviolet light is absorbed by a phosphor coating inside the lamp, causing it to produce visible light. This process produces much less heat than incandescent lights, but some energy is still lost creating ultraviolet light only to be converted into the visible spectrum. Further, the use of mercury vapor, even at the low levels present in most fluorescent bulbs, poses potential health and environmental risks.
Solid-state lighting is another alternative technology that could potentially displace incandescent lighting in many applications. In particular, light-emitting semiconductor devices, such as light-emitting diodes (LEDs), produce visible light by the electroluminescence of a semiconductor material in response to an electrical current. This process creates visible light with fewer inefficient energy losses, such as heat generation. In addition, light-emitting devices can be highly durable, generally have a life expectancy that is many times that of either incandescent or fluorescent lights, and their relatively small size allows them to be used in a wide variety of configurations.
Despite these advantages, however, light-emitting devices have not yet been widely accepted in the marketplace as a replacement for other forms of lighting. In combination with the relatively higher cost of the technology presently, this slow rate of acceptance is further thought to be a result of the fact that light-emitting devices produce light in a different way than either incandescent or fluorescent lights. Specifically, the light produced by light-emitting devices is highly directional, meaning that the light emitted tends to be rather focused in a particular direction. Thus, the technology is naturally suited for use in flashlights and other unidirectional applications, but it is not readily configurable to distribute uniform lighting to a wide area.
For example, previous attempts to create LED lighting fixtures have generally involved providing a planar array of LEDs. Although such arrays provide ample lighting, the light emitted tends to appear non-uniform because of “hot spots” of light intensity corresponding to each of the LEDs in the array. In addition, no light is cast behind the array, effectively creating a spotlight effect. As a result, it is thought that many individuals would not consider such fixtures because they would not provide the same kind of light as the incandescent lights to which they have become accustomed.
Accordingly, there exists a long-felt need for light-emitting device multi-chip lighting fixtures that provide an efficient alternative to incandescent and fluorescent lamps, but which also provide omni-directional lighting that has a substantially uniform luminous intensity in all directions.